1. Technical Field
The present disclosure relates to an optical lens assembly, and more particularly to a photographing optical lens assembly.
2. Related Art
In recent years, with the prosperity of photographing optical lens assemblies, the demand for compact photographing cameras boosts exponentially. The photo-sensing device, e.g. a sensor, of an ordinary photographing camera is commonly selected from a charge coupled device (CCD) and a complementary metal-oxide semiconductor (CMOS) device. In addition, as the advancing semiconductor manufacturing technology enables the minimization of the pixel size of sensors and the development of electronic products is heading toward full functionality and getting light, thin, short and small, the standards for the image quality of the photographing optical lens assemblies are rapidly raised.
In consideration of the aberration correction, the lens assembly of a conventional mobile electric device usually consists of three lens elements where the refractive power of the middle lens element is negative and those of the rest of the lens elements are positive. However, although the length of the lens assembly is reduced, the space of the photographing optical lens assembly available for forming image is also reduced. Additionally, the reduced space makes it difficult to incorporate the three lens elements into the photographing optical lens assembly. Therefore, the lens elements must become even thinner. However, when the lens element gets thinner, the uniformity of the lens thickness becomes worse, in terms of lens manufacturing by plastic injection molding.
A photographing optical lens assembly only with two lens elements is provided to effectively shorten the total length of the photographing optical lens assembly and improve the yield rate of the lens elements. For example, U.S. Pat. No. 7,525,741 discloses a two-piece optical lens system for taking image, comprising a first lens element with positive refractive power and a second lens element with negative refractive power in order from the object side to the image side. Although such arrangement enables the two-piece optical lens system to provide images having good resolution, it is difficult to shorten the total optical length of the two-piece optical lens system since the first lens element is a crescent lens having limited refractive power. Therefore, the inventors recognize that there is a need for a photographing optical lens which can be manufactured easily and has short optical length and low sensitivity.